What Causes My Car Engine to Overheat

I drive a 2003 Volkswagen Passat. Yesterday I was making a long trip home and about 20 minutes into the trip the car said it was overheating. The coolant level was fine, and as soon as we would pull over the temperature would drop back to normal (before we even got to a complete stop.) Later in the trip it stopped cooling down when we would pull over and there was a sort of popping/gurgling noise that sounded like it was sort of behind the dash.Took it to the mechanic today and they have cleaned the radiator, checked the head gasket, etc. and they are baffled.

Any ideas?

Hi there,

The VERY first thing that needs to be done is a "cooling system pressure test" this will determine if there is a coolant leak in the system. You want to check the coolant level INSIDE the radiator, not just what is in the plastic jug on the side of the engine.

This car is pretty new still, is it under warranty or are there high miles? Since you mentioned that it ran hot while you were driving, and as soon as you pulled over and slowed down the temperature returned to normal...my first thought would be that there is lack of coolant circulation. Low coolant level can also cause lack of circulation, so make sure the radiator is FULL.

If the coolant level is full, check the temperature of the radiator with the engine HOT. Caution, do not burn yourself!!! Start at the top of the radiator in the center and feel it with your handit should be very hot, move down the center of the radiator with your hand, it should remain pretty hot. If the bottom of the radiator is MUCH cooler than the top, you have a restriction in the radiator and you probably need to replace the radiator.

Same scenario as above, with engine hot - if the top and the bottom of the radiator seem warm but not HOT...I would replace the thermostat as a guess. Something is not allowing the coolant to flow through the system properly.

I would NOT expect a 3 year old car to have a restricted radiator (caused by rust or calcium deposits) but a faulty thermostat is possible.

Your car is also equipped with an electric cooling fan located near the radiator, next time it runs hot pull over, get out of the vehicle with the engine running and make sure this electric fan is ON. It will come on when the engine heats up and go off when not needed, you might also have another electric fan near the radiator that will be for the a/c compressor and should be on when the a/c is ON.

The noise you hear could just be the coolant inside the engine and the heater core (located inside the dash on the passenger side) boiling...which makes the sound you describe. Next time it runs hot, turn on the heater full blast, it will probably reduce the engine temperature enough so you dont have to pull over.

Of course it only take a few seconds of severe engine overheating to damage the engine, so when in doubt pull over and turn off the engine.

Auto Repair advice and Car repair questions answered. www.trustmymechanic.com/

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